Gastric cancer is the most common malignant tumor found in the gastrointestinal tract in Japan and Southeast Asia, and gastric cancer ranks in second place in cancer mortality in the world (Parkin et al. 1999). Although the prognosis for gastric cancer has improved by developments in diagnostic techniques and treatment methods of gastric cancer, the main cause of recurrence that occurs after curative resection of the advanced cancer is peritoneal dissemination. As to the prognosis for gastric cancer that has invaded to the gastric serosa, the 5-year survival rate is as low as 35% (Yamazaki et al. 1989). In such malignant properties of gastric cancer cells, metastasis to the peritoneum is a particularly complex phenomenon, which involves many steps and numerous genes. There are reports suggesting that adhesion molecules, apoptosis-related genes, and other genes are deeply involved in peritoneal dissemination of gastric cancer (Tahara et al., 1996, 2000; Yawata et al., 1998). However, elucidation of the mechanism of gastric cancer metastasis needs further investigations. Although it is known that escape of primary tumor cells from the basal layer and resistance to apoptosis are enhanced by changes in expression of genes that are suspected to be related to metastatic potential of cancer, the details of the mechanism are still unknown.
In order to study the mechanism of peritoneal dissemination of gastric cancer, Park et al. established SNU-1, SNU-5, SNU-16, and SNU-719 cell lines from the primary focus and other cancer cell lines from ascites fluid (Park et al., 1990, 1994). SNU cell lines have been studied particularly intensively. For example, it has been confirmed that cMET is amplified in SNU-16, overexpression of TGF-β2-type receptor, CEA, CA19-9, and c-erbB2 is observed in SNU-1, SNU-5, and SNU-16, K-sam is amplified in KATO-III cells (Katoh et al., 1992), and expression of E-cadherin is reduced in GT3TKB (Tamura et al., 1996). However, common gene changes in metastatic gastric cancer cells have not yet been clarified.
Despite the fact that a plurality of genes are known to participate cooperatively in cancer metastasis, only the relationship between a single gene or a few genes and metastasis has been reported. Further, the difference of metastatic potential of primary cancer focus is considered to be due to a difference in combination of expressed genes. For this reason, an analysis of gene expression in gastric cancer cells having different metastatic potential in respect of the degree of metastasis and metastasized sites is important for elucidation of the mechanism of peritoneal dissemination of gastric cancer.